Method of reducing stress level in animals

A method of reducing stress level in animals, the method comprising:

• sealable enclosing the animals in at least one chamber,
• exposing the animals to a gas mixture comprising oxygen and at least one type of physiologically inert gas,
• gradually decreasing oxygen concentration from a maximum level to a minimum level,
• gradually increasing the at least one physiologically inert gas concentration from a minimum level to a maximum level, and
• avoiding bringing the animals to a state of unconsciousness or death by the gas mixture throughout the at least one chamber;
• wherein the minimum level of the oxygen concentration is higher than an anesthetic causing concentration of oxygen for the animals,
• wherein the maximum level of the at least one physiologically inert gas concentration is between 90 to 97%, and
• wherein the gas mixture comprises a CO2 concentration lower than 5%;
• wherein the at least one chamber extends from a first position where the animals are received to a second position where at least one subsequent process takes place, where exposure to the gas is while the animals move from the first position towards the second position, the first position being the position where the concentration of the oxygen is maximum and where the concentration of the at least one physiologically inert gas is minimum, the second position being the position where the concentration of the oxygen is minimum and the concentration of the at least one physiologically inert gas is maximum;
• and
• wherein the at least one subsequent process includes at least one of a transport process, an examination process, and a treatment process.